Gram-negative bacteria have an outer membrane composed of a lipid bilayer inexistent in gram-positive bacteria, and thus tend to be more resistant to drugs, as compared with gram-positive bacteria, due to the problem of drug permeability. Gram-negative bacteria are also known to have a plurality of drug efflux proteins, which are known to be involved in drug resistance (Non-Patent Document 1). Furthermore, lipopolysaccharide (LPS), one of the main constituents of the outer membrane, greatly takes part in toxicity as an endotoxin.
Among gram-negative bacteria, Pseudomonas aeruginosa, in particular, is known to have a strong tendency to show natural resistance to various antimicrobial agents. Pseudomonas aeruginosa is a weakly toxic bacterial species which is found commonly and widely in natural environment and living environment, but is normally not pathogenic to healthy persons. However, Pseudomonas aeruginosa is a pathogenic microorganism causing a serious acute infection, such as sepsis, to patients with serious underlying diseases; patients, called compromised hosts, using immunosuppressants because of transplantation or the like; or patients subjected to medical care such as medical catheterization, endotracheal intubation, or surgical operation. Thus, Pseudomonas aeruginosa is one of important microorganisms causing opportunistic infections or nosocomial infections. In recent years, Pseudomonas aeruginosa, which has gained resistance to carbapenem drugs, quinolone drugs or aminoglycoside drugs expected to be essentially effective against Pseudomonas aeruginosa, has been clinically isolated in medical settings (Non-Patent Document 2). Moreover, multi-drug resistant Pseudomonas aeruginosa which has obtained resistance to all of these three types of drugs has been isolated (Non-Patent Document 3). Infections with multi-drug resistant Pseudomonas aeruginosa have posed worldwide major problems as intractable infectious diseases, because there have been few useful therapeutic drugs. Hence, there is a keen demand for the development of a drug having a novel mechanism of action.
UDP-3-O-acyl-N-acetylglucosamine deacetylase (LpxC) is an enzyme in charge of the synthesis of lipid A (hydrophobic anchor of LPS which is the constituent of the outer membrane). Lipid A biosynthesis consists of reactions in 10 stages, and LpxC catalyzes the second stage of the biosynthesis reactions to remove the acetyl group of UDP-3-O-acyl-N-acetylglucosamine (Non-Patent Document 4). Lipid A is a component essential for the formation of the outer membrane, and is consequently indispensable for the survival of gram-negative bacteria (Non-Patent Document 5). LpxC is one of the rate-determining important enzymes during the process of lipid A biosynthesis, and is an indispensable enzyme for lipid A biosynthesis. Thus, a drug inhibiting the activity of LpxC is highly expected to be capable of becoming an antimicrobial agent effective against gram-negative bacteria including Pseudomonas aeruginosa, particularly against drug resistant Pseudomonas aeruginosa, because such a drug has a mechanism of action different from those of conventional drugs.
LpxC inhibitors have hitherto been known from Patent Documents 1 to 4 and Non-Patent Documents 6 to 10 teaching inhibitors with amide structures, Patent Document 5 teaching an inhibitor with a urea structure, and Patent Document 6 teaching an inhibitor with an ether structure. However, the compound of the present invention is not known to have LpxC-inhibiting activity.